Abstract: Preparation of PS/PMMA composite materials by adding styrene butadiene rubber (SBR) was performed by in-situ two steps polymerization. The effect of the amount of SBR scattering substance on the optical properties of composite materials was investigated. The results indicated that the addition of SBR powder could have a synergistic effect with the MMA pre-polymer. The haze curve of the sample versus pre-polymeric MMA’s amount and SBR’s amount showed an oscillating variation relationship. The transmittance curves of the sample versus pre-polymeric MMA’s content was also an oscillating variation relationship，but the transmittance curve of the sample versus SBR’s content was not apparent oscillating variation relationship. The morphology of the composite materials was characterized with SEM. The surface of a notched sample showed that SBR particles were uniformly dispersed in the matrix.